Function execution model in Azure - Step-by-Step Execution

Process Flow - Function execution model

Trigger Event

↓

Function Host Receives Event

↓

Function Runtime Starts

↓

Function Code Executes

↓

Function Returns Result

↓

Host Sends Response or Continues

↓

Function Instance Idle or Terminates

This flow shows how an Azure Function starts from an event trigger, runs the code, returns a result, and then waits or stops.

Execution Sample

Azure

trigger -> function start -> execute code -> return result

This sequence shows the steps Azure Functions follow when triggered by an event.

Process Table

Step	Action	State Before	State After	Notes
1	Trigger event received	No active function	Function host ready	Event triggers function start
2	Function runtime starts	Function host ready	Function code loaded	Runtime prepares environment
3	Function code executes	Code loaded	Code executed	Function logic runs with input
4	Function returns result	Code executed	Result ready	Output prepared for caller
5	Host sends response	Result ready	Response sent	Caller receives function output
6	Function instance idle	Response sent	Waiting or terminated	Function waits for next trigger or stops

💡 Function completes execution and either waits for next event or terminates

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Function Host	Inactive	Ready	Ready	Ready	Idle or Terminated
Function Code	Not loaded	Loaded	Executed	Executed	Idle or Terminated
Input Event	None	Received	Used	Used	Cleared
Output Result	None	None	None	Ready	Sent

Key Moments - 3 Insights

Why does the function host start before the function code executes?

The function host prepares the environment and runtime needed to run the function code, as shown in steps 1 and 2 of the execution_table.

What happens to the function instance after it returns a result?

After returning a result, the function instance either waits idle for the next trigger or terminates, as shown in step 6 of the execution_table.

Is the input event still available after the function executes?

No, the input event is used during execution and then cleared after the function returns the result, as tracked in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the state of the function host after step 2?

A Inactive

B Idle

C Ready

D Terminated

💡 Hint

Check the 'State After' column for step 2 in the execution_table.

At which step does the function code actually run?

A Step 3

B Step 2

C Step 1

D Step 5

💡 Hint

Look for 'Function code executes' in the Action column of the execution_table.

If the function instance terminates immediately after sending the response, which step describes this?

A Step 5

B Step 6

C Step 4

D Step 3

💡 Hint

Step 6 shows the function instance becoming idle or terminated.

Concept Snapshot

Azure Function execution model:
- Trigger event starts function
- Host prepares runtime environment
- Function code runs with input
- Function returns output
- Host sends response
- Function instance waits or stops

Full Transcript

Azure Functions start when an event triggers them. The function host receives this event and prepares the runtime environment. Then, the function code executes using the input from the event. After execution, the function returns a result. The host sends this result back to the caller. Finally, the function instance either waits idle for the next trigger or terminates if no further events occur.